Impact mechanisms such as pneumatic impact wrenches and the like are well known in the prior art. One such device is disclosed in U.S. Pat. No. 3,661,217 to Maurer, incorporated herein by reference. Such prior art impact mechanisms generally include a motor having an output shaft that rotates a cage member. The cage member journals a power output shaft or anvil at a bore of the cage member. The anvil includes either a single jaw or a pair of jaws depending on the number of hammers or dogs. Each hammer is pivotally coupled to the cage member on a longitudinal hammer pin such that the hammer pivots with respect to, and rotates with, the cage member. As the cage member rotates, hollow interiors of the hammers engage with the jaws to engage the anvil and to transmit an impact to the anvil.
In such prior art configurations, the end wall of the cage member nearest the motor will commonly crack and fail due to high impact stresses. The inventors have discovered that such damage is due in part to the use of support holes for the hammer pins which extend completely through the end wall of the cage member. The present invention provides a design improvement that overcomes the above-described disadvantages of the prior art.